Transfer ribonucleic acid sulfurtransferase is an enzyme which thiolates tRNA at the macromolecular level by transferring the sulfur moiety from beta-mercaptopyruvate or cysteine to specific bases on the tRNA molecule. This project deals with: 1) the isolation and purification of tRNA sulfurtransferase from rat brain and rat liver; 2) investigation of the mechanism of action of this enzyme; 3) study of variation of the level of this enzyme in various physiological states, in tissue differentiation, and in neoplasia. BIBLIOGRAPHIC REFERENCES: Harris, M.A., Wong, T.-W., and Morris, H.P. Comparative studies of tRNA sulfurtransferase activities in normal rat liver and Morris hepatomas. Fed. Proc 34: 612, 1975. (Abstract) Wong, T.-W., Harris, M.A., and Morris, H.P. The presence of an inhibitor of tRNA sulfurtransferase in Morris hepatomas. Biochem. Biophys. Res. Commun. 65: 1137-1145, 1975.